When stricture or obstruction (thrombus) of a coronary artery of the heart occurs, bypass vascular transplantation surgery for bridging over the stricture or obstruction is conducted. This surgery makes an incision in a junctional part of a blood vessel using a medical knife, cuts with scissors along this incision to enlarge it to a desired size, and sutures and connects an end of a blood vessel for transplantation to the enlarged part.
The medical knife used in this case may be the medical knife described in Patent Document 1, for example. FIG. 5 is a diagram illustrating a conventional medical knife described in Patent Document 1. This medical knife 51 includes a cutting portion 53 accompanied in a knife holder 54, and is used with the knife holder 54 attached to an attaching part 52a that extends from a metal handle 52.
Here, there are two types of the attaching part 52a: one that is at an angle with the handle 52, and the other that is at no angle with the same. Moreover, according to the shape of the knife holder 54, there are two types of the cutting portion 53: one that is at an angle with the attaching part 52a, and the other that is at no angle with the same. Note that the attaching part 52a of the medical knife illustrated in FIG. 5 is at no angle with the handle 52 and the cutting portion 53 is at an angle with the attaching part 52a. 
The medical knife 51 having such a configuration can have diverse angles of the cutting portion 53 with the handle 52 in accordance with a combination of the attaching part 52a having or not having an angle and the knife holder 54 having or not having an angle, and can therefore be used for different purposes according to the position of the diseased part or preference of the surgeon.
In a large-scale operation such as heart surgery, several kinds of the medical knife 51 and other tools etc. are used in this manner. When replacing the medical knife 51 or changing it to another tool, etc., the medical knife 51 in hand is once placed on a stand. In this case, the medical knife 51 illustrated in FIG. 5 is used with a cutting blade facing upward when making an incision. As a result, when laying this medical knife 51 on the stand, it is generally placed with the cutting blade facing upward. However, if the cutting blade of the medical knife 51 placed on the stand is facing upward, there is a risk of injury by the cutting blade of the medical knife 51 when the surgeon places his/her hand on the stand or when holding another knife or tool, etc. in his/her hand.
Moreover, since the cutting portion 53 of the medical knife 51 used to form an incision in a coronary artery often has an angle with the handle 52, the medical knife 51 may roll when placing it on the stand, thereby possibly making the cutting blade of the cutting portion 53 touch the stand, and damaging the cutting blade at that time.